Chitin is the second most abundant polymer on earth after cellulose, it is common waste in seafood factories and (as a natural polymer) it is biodegradable. However its processing in the laboratory for fabrication produce a hydrogel material with poor mechanical properties.
Chitin is a broadly employed polymer in nature. It is found in the walls of fungi, in mollusk shells and the exoskeleton of arthropods. It provides many structural uses due to its mechanical properties. Many attempts have carried out to employ the polymer as a substitute of current synthetic plastics; however it has not been possible to reproduce its exceptional natural properties in the lab. The lack of success results from the failure to appreciate the important structural role played by chitin-associated proteins that are present within natural structures, and the laminar microarchitecture of naturally occurring materials produced by living organisms.
The main protein present both in the mollusk shells and the arthropods exoskeleton, which plays a fundamental role in the structural integrity of the shell, has an amino acid sequence similar to that of silk fibroin.
Chitin and protein (such as silk fibroin) blends have been produced in the prior art by the simple mixing of both materials in solution. These processes are intent on producing consistent mixtures of Chitin/Chitosan and silk fibroin by mixing both polymers in solution and casting the mixture. That approach does not yield any improvement in the mechanical properties of mixture over the components, and typically produces an even weaker material due to the interaction of both polymers, which interferes with each other's molecular and crystal structure.
Silk Fibroin is well known polymer material. Silk provides an important set of material options for biomaterials and tissue engineering because of the impressive mechanical properties, biocompatibility and biodegradability. Silk polymer and Silk Fibroin includes silkworm fibroin and insect or spider silk protein (Lucas et al., Adv. Protein Chem 13: 107-242 (1958)). Preferably, fibroin is obtained from a solution containing a dissolved silkworm silk or spider silk. Generally, fibroin polymer (or protein) from silk has been treated to substantially remove sericin. The silkworm silk protein is obtained, for example, from Bombyx mori, and the spider silk is obtained, for example, from Nephila clavipes. In the alternative, silk proteins suitable for use in the present invention can be obtained from a solution containing a genetically engineered silk, such as from bacteria, yeast, mammalian cells, transgenic animals or transgenic plants. See, for example, WIPO Publication No. WO 1997/108315 and U.S. Pat. No. 5,245,012 which are hereby incorporated by reference herein.
Silk fibroin has excellent film-forming capabilities and is also compatible for use in the human body. Silk fibroin films, without further manipulation or treatment, are soluble in water because of dominating random coil protein structures. The structural features of the protein can be transformed from random coil to beta-sheet structure by several treatments, including mechanical stretching, immersion in polar organic solvents, or curing in water vapor. Without wishing to be bound by a theory, use of highly concentrated silk solutions is also known to promote beta-sheet transition from random coils. This structural transition results in aqueous insolubility, thus providing options for the use of the material in a range of biomedical and other applications. Some pure silk fibroin films tend, over time, to become stiff and brittle in the dry state, however, exhibiting impressive tensile strength but low ductility. Further, dissolved Silk Fibroin can be mixed with particulates to produce a homogeneous mixture that can be formed into implantable structures. Methods of making silk polymer structures and Silk Fibroin films are shown in WIPO Publication Nos. WO 2009/0100280 and WO 2010/0042798, both which are hereby incorporated by reference herein.